v2.4.0.6
Segment and Significant Customer Information (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2010
Sep. 30, 2010
Jun. 30, 2010
Mar. 31, 2010
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Revenues from external customers $ 1,459 $ 2,209 $ 1,633 $ 1,499 $ 1,471 $ 2,130 $ 1,430 $ 1,514 $ 6,800 $ 6,545 $ 6,463
Intersegment revenues                 0 0 0
Total operating revenues                 6,800 6,545 6,463
Commodity Margin                 2,474 2,391 2,461
Add: Mark-to-market commodity activity, net and other                 (33) [1],[2] 171 [1] 100 [1]
Plant operating expense                 904 868 868
Depreciation and amortization expense                 550 570 456
Sales, general and other administrative expense                 131 151 174
Other operating expenses                 77 [3] 91 [3] 96 [3]
Impairment losses                   116 4
Gain (Loss) on Disposition of Assets                 0 (119) 0
(Income) from unconsolidated investments in power plants                 (21) (16) (50)
Income from operations 196 403 183 18 89 554 108 150 800 901 1,013
Interest expense, net of interest income                 751 802 799
Loss on interest rate derivatives                 145 223 0
Debt extinguishment costs and other (income) expense, net                 115 106 89
Income (loss) before income taxes and discontinued operations                 (211) (230) 125
Lease levelization                 12    
Contract amortization                 8    
RGGI compliance and other environmental costs                 10 9 5
West [Member]
                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Revenues from external customers                 2,372 2,525 3,311
Intersegment revenues                 12 12 28
Total operating revenues                 2,384 2,537 3,339
Commodity Margin                 1,061 1,080 1,245
Add: Mark-to-market commodity activity, net and other                 113 [1],[2] 69 [1] 143 [1]
Plant operating expense                 380 351 408
Depreciation and amortization expense                 192 207 188
Sales, general and other administrative expense                 43 55 66
Other operating expenses                 41 [3] 59 [3] 73 [3]
Impairment losses                   97 4
Gain (Loss) on Disposition of Assets                   0  
(Income) from unconsolidated investments in power plants                 0 0 (32)
Income from operations                 518 380 681
Texas [Member]
                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Revenues from external customers                 2,306 2,162 1,816
Intersegment revenues                 23 22 63
Total operating revenues                 2,329 2,184 1,879
Commodity Margin                 469 504 644
Add: Mark-to-market commodity activity, net and other                 (102) [1],[2] 89 [1] (40) [1]
Plant operating expense                 235 285 232
Depreciation and amortization expense                 135 150 129
Sales, general and other administrative expense                 43 38 63
Other operating expenses                 3 [3] 2 [3] 14 [3]
Impairment losses                   0 0
Gain (Loss) on Disposition of Assets                   (119)  
(Income) from unconsolidated investments in power plants                 0 0 0
Income from operations                 (49) 237 166
North [Member]
                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Revenues from external customers                 1,336 978 558
Intersegment revenues                 7 6 16
Total operating revenues                 1,343 984 574
Commodity Margin                 704 535 268
Add: Mark-to-market commodity activity, net and other                 (13) [1],[2] 21 [1] 46 [1]
Plant operating expense                 177 138 91
Depreciation and amortization expense                 138 111 67
Sales, general and other administrative expense                 24 45 18
Other operating expenses                 30 [3] 28 [3] 30 [3]
Impairment losses                   0 0
Gain (Loss) on Disposition of Assets                   0  
(Income) from unconsolidated investments in power plants                 (21) (16) (18)
Income from operations                 343 250 126
Southeast [Member]
                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Revenues from external customers                 786 880 778
Intersegment revenues                 135 138 97
Total operating revenues                 921 1,018 875
Commodity Margin                 240 272 304
Add: Mark-to-market commodity activity, net and other                 1 [1],[2] 22 [1] (5) [1]
Plant operating expense                 141 123 134
Depreciation and amortization expense                 90 109 80
Sales, general and other administrative expense                 22 12 27
Other operating expenses                 5 [3] 4 [3] 11 [3]
Impairment losses                   19 0
Gain (Loss) on Disposition of Assets                   0  
(Income) from unconsolidated investments in power plants                 0 0 0
Income from operations                 (17) 27 47
Consolidation and Elimination [Member]
                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Revenues from external customers                 0 0 0
Intersegment revenues                 (177) (178) (204)
Total operating revenues                 (177) (178) (204)
Commodity Margin                 0 0 0
Add: Mark-to-market commodity activity, net and other                 (32) [1],[2] (30) [1] (44) [1]
Plant operating expense                 (29) (29) 3
Depreciation and amortization expense                 (5) (7) (8)
Sales, general and other administrative expense                 (1) 1 0
Other operating expenses                 (2) [3] (2) [3] (32) [3]
Impairment losses                   0 0
Gain (Loss) on Disposition of Assets                   0  
(Income) from unconsolidated investments in power plants                 0 0 0
Income from operations                 5 7 (7)
PJM Settlement, Inc. [Member]
                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Major customer revenue                 742    
Major customer receivables                 $ 28    
Number of significant customers                 1    
[1] Mark-to-market commodity activity represents the unrealized portion of our mark-to-market activity, net, included in operating revenues and fuel and purchased energy expense on our Consolidated Statements of Operations for the years ended December 31, 2011, 2010 and 2009, as well as a non-cash gain from amortization of prepaid power sales agreements for the year ended December 31, 2009.
[2] Includes $12 million of lease levelization and $8 million of contract amortization for the year ended December 31, 2011 related to contracts that became effective in 2011.
[3] Excludes $10 million, $9 million and $5 million of RGGI compliance and other environmental costs for the years ended December 31, 2011, 2010 and 2009, respectively, which are components of Commodity Margin.